Hi Manikandan, JSTL is a set of custom tags which have been made by somebody else to make our lives easier.Remember, JSTL are not a part of JSP 2.0 specs.You have to explicitly put the jstl jar file in your WEB-INF/lib directory inorder to use it.

In the question tag <c ut ... /> may be not JSTL "out" tag, as there is no information about that, but any custom tag which just looks the same. Prefix "c" is not reserved so you can use it to bind any custom tag library.